JPH07157838A - Method for producing sintered magnetic alloy and powder for sintered magnetic alloy - Google Patents

Abstract

(57) [Abstract] [Purpose] O contained in powder is reduced to CO by heating during sintering.
Provided is a manufacturing method for removing by reaction to enhance the magnetic properties of a sintered magnetic alloy. [Structure] O contained in the powder for a sintered magnetic alloy and C for causing a CO reaction are added and mixed in the form of carbon black powder and in an amount corresponding to the contained O, and this is mixed under vacuum or at 20 Torr or less. By sintering in a slight pressure atmosphere, O in the powder is removed by the CO reaction during the sintering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered magnetic alloy and a powder for a sintered magnetic alloy.

[0002]

2. Description of the Related Art Iron-chromium magnetic alloys have been developed as rust-resistant soft magnetic alloys, also called electromagnetic stainless steels, and widely used for electromagnetic valves, electromagnetic cores and other applications. Iron-chromium-based sintered magnetic alloys formed by sintering powders have also been put into practical use and various studies have been conducted.

By the way, since the powder for this kind of magnetic alloy contains a considerable amount of Cr, the powder is hard, and the compressibility is inferior, so that the green compact is low and therefore the sintered density is low and the magnetic properties are sufficient. There is a problem that is difficult to demonstrate.

[0004] In addition, since Cr and Si oxides are present on the surface of the powder, this powder inhibits the sintering action and inhibits the growth of crystal grains and the spheroidization of the pore shape, whereby the sintered magnetic alloy. However, there is also a problem that it is difficult to exhibit the magnetic characteristics sufficiently.

In this case, the O contained in the powder
When graphite as a C source is added to a metal powder in an amount necessary to cause a CO reaction with CO, or if C is alloyed and contained in the powder in advance, the above CO reaction occurs during sintering. As a result, O dissolved in the powder surface and the alloy can be removed, and the magnetic characteristics of the sintered magnetic alloy can be improved. However, the CO reaction in this case occurs when sintering is performed in a vacuum or in a low pressure atmosphere up to about 20 Torr.

[0006]

However, when graphite is added to and mixed with the metal powder, since graphite itself is a material having lubricity, vibration during storage or transportation of the mixed powder of the metal powder and graphite or during molding is performed. As a result, weight segregation is likely to occur, which causes unevenness in the actual addition amount of each product, resulting in a variation in performance.

On the other hand, when C is alloyed with powder in advance, the hardness of the powder becomes more and more hard, and an annealing step is required at the time of manufacturing the powder, so that the powder price becomes high.

[0008]

The invention of the present application has been made in order to solve such a problem, and the gist thereof is to cause the reaction of O and CO contained in the powder for a sintered magnetic alloy. By adding and mixing C in the form of carbon black powder and in an amount corresponding to the contained O and sintering this in a vacuum or a slight pressure atmosphere of 20 Torr or less, the CO reaction in the powder during the sintering is performed. Is to remove O.

[0009]

As described above, according to the present invention, carbon black powder as a C source is added to and mixed with alloy powder, and this is sintered in a vacuum or slight pressure atmosphere.

Here, the carbon black powder is a soot-like substance formed by burning or thermally decomposing a hydrocarbon or a compound containing carbon in a state where the air supply is insufficient, and the channel may differ depending on the raw material and the manufacturing method. Various types such as black, furnace black and thermal black are known. This carbon black powder is generally widely used for applications such as rubber reinforcing agents, printing inks and paints.

The carbon black powder is characterized in that it contains a small amount of oil together with the carbon component, and this oil has a function of attaching particles to each other in the powder.

Therefore, when such carbon black powder is added to and mixed with the alloy powder as a C source, each powder particle is fixed to a certain extent with a weak adhesive force unlike the case of adding the above graphite, and it is caused by vibration during storage and transportation. It does not cause weight segregation. Therefore, when the individual products are actually manufactured, unevenness of the added amount does not occur, and therefore, variations in product performance can be prevented.

Further, when carbon black is added, unlike the case where C is alloyed in the powder, the powder itself does not become hard, so the above-mentioned annealing step is not particularly required, and therefore the powder price is low. Can be suppressed.

On the other hand, since the adhesive force of the carbon black powder based on the oil content is slight, the fluidity of the powder for sintered alloy is not particularly impaired during the molding, and the molding can be performed well.

Further, the carbon black particles are not easily separated from the metal powder particles by the above oil content, which is advantageous in terms of dust countermeasures.

In the present invention, C: 0.05% or less, Cr: 30
%, Si: 4% or less, Mo: 4% or less, the balance being an unavoidable impurity, and an alloy powder having a composition of Fe, which is particularly suitable for producing a sintered magnetic alloy.

Here, C is 0.05% or less and Cr is 30%.
The reasons for limiting to the following are as follows. That is, C is 0.
If it is more than 05%, the powder becomes hard and the moldability becomes poor.
On the other hand, if the Cr content exceeds 30%, the powder is hardened and the moldability is remarkably deteriorated, resulting in poor practicality. Further, the amount of oxygen increases remarkably, and the effect of adding carbon black cannot be obtained.

The reason why each of Si and Mo is 4% or less is that when Si> 4%, the powder becomes hard and the moldability,
Sinterability deteriorates significantly. In addition, Si oxide is increased and the contribution to magnetism is reduced. Further, if Mo> 4%, the powder becomes hard, the moldability is deteriorated, and the magnetism is adversely affected.

In the present invention, the amount of carbon black powder to be added should be basically determined according to the amount of oxygen in the metal powder, but generally 0.05% to 100% of alloy powder. It is desirable to add in the amount of (powder O% -0.03 x Si%). If it is less than 0.05%, it is difficult to remove O in the powder sufficiently.
If it is more than −0.03 × Si%), C remains in the powder and carbide is generated. This carbide adversely affects the magnetic properties of the sintered magnetic alloy.

[0020]

EXAMPLES Examples of the present invention will be described in detail below.

[0021]

[Table 1]

Metal (alloy) powders (100 mesh under) having various compositions shown in Table 1 were manufactured by a water spray method.
When this powder was molded and sintered and the sintered density and the maximum magnetic permeability were measured, the results shown in Table 2 were obtained.
The molding is performed under a pressure of 7 t / cm ³ , and the sintering is performed in a vacuum at 500 ° C. for 30 minutes +5 TorrN ₂ at 1200 ° C. × 60.
It went under the condition of minute.

On the other hand, carbon black powder (type is furnace black having a particle size of 28 nanomicrons) was added to the above various metal powders, and this was molded and sintered to measure the sintered density and the maximum magnetic permeability. The results shown in 2 were obtained.

[0024]

[Table 2]

In the table, No. No. 8 is hard because it is a high-C powder, and cannot be molded without annealing. Therefore, the result when annealing is performed is shown.

No. in the above table. The sample No. 4 was molded and sintered by changing the amount of carbon black added, and the oxygen, carbon and magnetic properties finally contained were measured, and the results were as shown in FIG.

From the above results, the addition of carbon black powder improves the magnetic properties of the sintered magnetic alloy,
In addition, especially from the results of FIG. 1, the addition of carbon black powder reduces the oxygen content of the magnetic alloy, and along with this, the magnetic characteristics are improved. Furthermore, there is an appropriate range for the addition amount of carbon black powder. If the above addition is made, the magnetic properties tend to decrease, and the amount of residual C is the standard. That is, if C of the added carbon black is left in the sintered magnetic alloy, the magnetic properties become Shows a tendency to decrease, and therefore the proper amount of carbon black powder added is such that oxygen contained in the powder is consumed during sintering and C is not left.

When the carbon black powder was added and mixed, the amount of C in the powder of each part after the mixed powder was transported by a truck (traveled for about 500 km) was measured, and no particular weight segregation was observed. Similarly, when powder was compacted by an automatic molding machine and analyzed for the amount of C, it was confirmed that weight segregation did not particularly occur.

The embodiment of the present invention has been described in detail above, but this is merely an example, and the present invention is generally applicable to the production of various sintered magnetic alloys, etc. within a range not departing from the gist thereof. It can be implemented in variously modified modes.

[Brief description of drawings]

FIG. 1 shows the amounts of carbon black added and the contents of oxygen and carbon in magnetic alloys obtained in Examples of the present invention,
It is a figure showing the relationship with a magnetic characteristic.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C22C 38/00 304 38/22 H01F 1/22

Claims (3)

[Claims] 1. O and CO contained in a powder for a sintered magnetic alloy.
C for causing the reaction is added and mixed in the form of carbon black powder and in an amount corresponding to the contained O, and this is sintered in a vacuum or a slight pressure atmosphere of 20 Torr or less, so that at the time of the sintering. A method for producing a sintered magnetic alloy, characterized in that O in the powder is removed by the CO reaction. 2. The manufacturing method according to claim 1, wherein the alloy powder contains C: 0.05% or less, Cr: 30% or less, Si: 4% or less, Mo: 4% or less, and the balance inevitable impurities. A method for producing a sintered magnetic alloy, characterized in that the composition is composed of Fe and Fe. 3. C: 0.05% or less by weight, Cr:
A powder for a sintered magnetic alloy, which is obtained by mixing carbon black powder with an alloy powder having a composition of 30% or less, Si: 4% or less, Mo: 4% or less, the balance unavoidable impurities, and Fe.